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27 Cards in this Set
- Front
- Back
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Properties of semi-conductors
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-conduct only if high enough voltage is present
-typically covalent solids(Si) -Conduct is high if temp is high |
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Properties of insulators
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non-conductive
typically ionic solids (NaCl) |
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What is the new theory that explains electronic properties of materials?
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Molecular orbital theory
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What does the MO theory explain?
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-electronic properties of all types of solids
-biologically relevant reactivity -bonding, reactivity and color in a huge array of compounds |
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What is the fundamental starting point of MO's?
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individual atomic orbitals will overlap, interact and form new molecular orbitals
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Because of the MO theory...
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the electrons in molecules can spread out over the entire molecule via the MOs
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The number of AOs must equal..
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the final number of MOs
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What are geographical representations of electron wavefunctions?
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Orbitals
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How many electrons can occupy any orbital?
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2 e's
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Adding wave functions=
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constructive interference and there WILL be electron density between atoms
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Subtracting wave functions=
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destructive interference and there WILL NOT be electron density between atoms because of wave cancelation
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What does more nodes mean?
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higher energy thus less stable
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Bond-order?
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# bonding-#antibonding electrons/ 2
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HOMO=
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highest occupied molecular orbital
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LUMO=
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lowest unoccupied molecular orbital
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Paramagntic
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has unpaired electrons attracted to a magnetic field
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What is the Band theory?
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-a continuous band of orbitals. The electrons can occupy any space in it
-region one moles worth of orbitals -space between atoms is about zero |
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Most metals have...
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a partially full band
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Explain what happens because lead has a partially full band
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the electrons have many places to jump so the electrons are excited so light is absorbed into the lead and thus the eye cannot see it
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Besides metals what else does the band theory apply to?
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MOs and covalent networks
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In semi-conductors the band gap is.. so...
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relatively small so it is easy to excite the electrons so it moves up in energy; can apply voltage to make the electrons conduct; gives rise to 2 states
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The bigger the band gap..
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the bigger the energy released
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Think liquid nitrogen lab.. explain what happens if the LED is cooled.. in terms of energy, bonds, wavelength. etc
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If LEDs are made cold, they become more dense. The band gap is increased so the bonds get stronger but the wavelength gets shorter
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Bonding orbitals are...
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additive
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Antibonding orbitals are those which...
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the waves cancel each other
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Give 2 examples where the valence bond theory provides and incomplete or no explanation or reasons why it isnt very explanative?
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- why O2 is paramagnetic
-why we dont have molecules such as He2 |
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Give an example why valence bond theory is still really useful?
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it shows how big molecules form
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